The present invention relates generally to semiconductor fabrication and, more particularly, to apparatus and methods for controlling the plasma behavior inside of plasma etching chambers.
In semiconductor manufacturing processes, etching processes, insulation film formation, and diffusion processes are repeatedly carried out. As is well known to those skilled in the art, there are two types of etching processes: wet etching and dry etching. Dry etching is typically implemented by using an inductively coupled plasma etching apparatus such as shown in FIG. 1A.
In the inductively coupled plasma etching apparatus shown in FIG. 1A, a reactant gas is first led into chamber 20 through a gas lead-in port (not shown). High frequency power is then applied from a power supply (not shown) to coil 17. Semiconductor wafer 11 is mounted on chuck 19 provided inside chamber 20. Coil 17 is held on the upper portion of the chamber by spacers 13, which are formed of an insulating material. In operation, high frequency (RF) current passing through coil 17 induces an electromagnetic current into chamber 20, and the electromagnetic current acts on the reactant gas to generate a plasma.
The plasma contains various types of radicals and the chemical reaction of the positive/negative ions is used to etch semiconductor wafer 11 itself or an insulation film formed on the wafer. During the etching process, coil 17 carries out a function that corresponds to that of the primary coil of a transformer while the plasma in chamber 20 carries out a function that corresponds to that of the secondary coil of the transformer. The reaction product generated by the etching process is discarded via exhaust port 15.
When etching one of the recently developed device materials (e.g., platinum, ruthenium, and the like), the reaction product generated may be a nonvolatile substance (e.g., RuO2). In some cases, the reaction product may adhere to surface 10a of TCP window 10. If the reaction product is conductive, then the film of reaction product on surface 10a may electrically shield the electromagnetic current in the chamber. Consequently, the plasma does not strike well after several wafers are etched and the etching process must be discontinued.
In an effort to avoid this problem, a method for sputtering the reaction product adhered to surface 10a of TCP window 10 by using the plasma has been developed. In the inductively coupled plasma etching apparatus shown in FIG. 1A, however, the electromagnetic current induced by the RF current generates a distribution voltage having a standing wave in the vicinity of TCP window 10. This is problematic because it causes the deposition and sputtering of the reaction product to become nonuniform.
FIGS. 1B and 1C illustrate the inherent nonuniformity of the deposition and sputtering on the TCP window in the inductively coupled plasma etching apparatus shown in FIG. 1A. In FIG. 1B, coil 17 is indicated by boxes having either an xe2x80x9cxxe2x80x9d or a xe2x80x9cxe2x97xafxe2x80x9d therein. The boxes having an xe2x80x9cxxe2x80x9d therein indicate that the coil extends into the page. The boxes having a xe2x80x9cxe2x97xafxe2x80x9d therein indicate that the coil extends out of the page. As shown in FIG. 1B, some portions of surface 10a of TCP window 10 are subjected to excess sputtering and other portions of the surface are subjected to excess deposition. Excess sputtering occurs in the regions where a relatively large amount of energy is added to the ions in the plasma because the amplitude of the acceleration voltage due to the standing wave at the location is high. As shown in the graph in the lower part of FIG. 1C, the amplitude of standing wave 24 is high at points 24a and 24b, which correspond to ends 17a and 17b, respectively, of coil 17, as shown in the upper part of FIG. 1C. Excess deposition occurs in the regions where only a relatively small amount of energy is added to the ions in the plasma because the amplitude of the standing wave is low. As shown in the graph in the lower part of FIG. 1C, the amplitude of standing wave 24 is low in the region proximate to point 22, which is the node of the standing wave.
Nonuniform deposition and sputtering on the TCP window is undesirable for a number of reasons. Excessive deposition is undesirable because, as discussed above, the presence of an electrically conductive film on the surface of the TCP window can electrically shield the electromagnetic current in the chamber and thereby disable the etching process. In addition, excessive deposition often causes particle problems (particles flake off on the wafer) and, consequently, increases the frequency with which the chamber must be subjected to dry and wet cleanings. Frequent cleaning of the chamber is particularly undesirable because it sacrifices the tool""s available up time and thereby reduces throughput. Excessive sputtering is undesirable because the ion bombardment can cause erosion of the TCP window, which is typically made of quartz or alumina. Such erosion not only shortens the lifetime of the TCP window, but also generates particles, which can contaminate the wafer and introduce unwanted chemical species into the process environment. The presence of unwanted chemical species in the process environment is particularly undesirable because it leads to poor reproducibility of the process conditions.
In view of the foregoing, there is a need for an inductively coupled plasma etching apparatus that prevents substantial deposition of electrically conductive reaction products on the surface of the TCP window without causing excess erosion of the TCP window.
Broadly speaking, the present invention provides an inductively coupled plasma etching apparatus that uniformly adds energy to the ions in the plasma in the vicinity of a wall of the chamber in which the plasma is generated.
In one aspect of the invention, a first type of inductively coupled plasma etching apparatus is provided. This inductively coupled plasma etching apparatus includes a chamber and a window for sealing a top opening of the chamber. The window has an inner surface that is exposed to an internal region of the chamber. A metal plate, which acts as a Faraday shield, is disposed above and spaced apart from the window. A coil is disposed above and spaced apart from the metal plate. The coil is conductively connected to the metal plate at a connection location that is configured to generate a peak-to-peak voltage on the metal plate that optimally reduces sputtering of the inner surface of the window while substantially simultaneously preventing deposition of etch byproducts on the inner surface of the window.
In one embodiment, the inductively coupled plasma etching apparatus further includes a coil input terminal for receiving RF power and a coil output terminal. In this embodiment, the connection location is defined between the coil input terminal and the coil output terminal. In one embodiment, the connection location is more proximate to the coil output terminal than to the coil input terminal. In one embodiment, the inductively coupled plasma etching apparatus further includes an RF generator, a match circuit network coupled between the RF generator and the coil input terminal, and a variable capacitor coupled between ground and the coil output terminal.
In one embodiment, the inductively coupled plasma etching apparatus further includes an oscillation circuit coupled to the metal plate. The oscillation circuit is controllable so that the peak-to-peak voltage on the metal plate may be adjusted. In one embodiment, the oscillation circuit includes a variable capacitor that can be adjusted to control the peak-to-peak voltage along a harmonic point. In another embodiment, the inductively coupled plasma etching apparatus further includes a voltage divider circuit coupled to the metal plate. The voltage divider circuit is controllable so that the peak-to-peak voltage may be adjusted. In one embodiment, the voltage divider circuit includes a variable capacitor that can be adjusted to control the peak-to-peak voltage along a plot that decreases the peak-to-peak voltage as capacitance of the variable capacitor increases.
In one embodiment, the inductively coupled plasma etching apparatus includes a chamber lid that is configured to have attached thereto the metal plate and the coil. The chamber lid may be attached by hinges that enable opening and closing of the chamber lid. When in a closed position, the chamber lid places the metal plate proximate to the window in preparation for operation.
In another aspect of the invention, a second type of inductively coupled plasma etching apparatus is provided. This inductively coupled plasma etching apparatus includes a chamber and a window for sealing a top opening of the chamber. The window has an inner surface that is exposed to an internal region of the chamber. A metal plate, which acts as a Faraday shield, is disposed above and spaced apart from the window. A coil is disposed above and spaced apart from the metal plate. The apparatus also includes a controller for externally applying a peak-to-peak voltage to the metal plate. The controller includes an oscillation circuit, a matching circuit, an RF generator, and a feedback control for monitoring the applied peak-to-peak voltage.
In one embodiment, the externally applied peak-to-peak voltage is adjustable so as to reduce sputtering of the inner surface of the window while substantially simultaneously preventing deposition of etch byproducts on the inner surface of the window. In one embodiment, the inductively coupled plasma etching apparatus further includes a coil input terminal for receiving RF power and a coil output terminal. In one embodiment, the inductively coupled plasma etching apparatus further includes an RF generator, a match circuit network coupled between the RF generator and the coil input terminal, and a variable capacitor coupled between ground and the coil output terminal.
In one embodiment, the metal plate is connected to the window by dielectric spacers. In one embodiment, the inductively coupled plasma etching apparatus includes a chamber lid that is configured to have attached thereto the metal plate and the coil. The chamber lid may be attached by hinges that enable opening and closing of the chamber lid. When in a closed position, the chamber lid places the metal plate proximate to the window in preparation for operation. When in an open position, the chamber lid places the metal plate away from the window for visual inspection of the window and servicing of the chamber.
In accordance with yet another aspect of the invention, a first method for optimizing operation of an inductively coupled plasma etching apparatus is provided. In this method, a chamber for etching a wafer is supplied. A window is attached to a top opening of the chamber. The window has an outer surface and an inner surface that is exposed to an inner region of the chamber. A coil is placed over the window and a metal plate is placed over the outer surface of the window. The metal plate is positioned in a spaced apart relationship between the coil and the outer surface of the window. The metal plate is conductively connected to a connection location on the coil. The connection location is between an input terminal and an output terminal and is optimally selected so as to produce substantially uniform incident ion energy proximate to the inner surface of the window. The substantially uniform incident ion energy is configured to reduce sputtering of the inner surface of the window while substantially simultaneously preventing deposition of etch byproducts on the inner surface of the window.
In accordance with a still further aspect of the invention, a second method for optimizing operation of an inductively coupled plasma etching apparatus is provided. In this method, a chamber for etching a wafer is supplied. A window is attached to a top opening of the chamber. The window has an outer surface and an inner surface that is exposed to an inner region of the chamber. A coil is placed over the window and a metal plate is placed over the outer surface of the window. The metal plate is positioned in a spaced apart relationship between the coil and the outer surface of the window. A controlled peak-to-peak voltage is applied to the metal plate so as to produce substantially uniform incident ion energy proximate to the inner surface of the window. The substantially uniform incident ion energy is configured to reduce sputtering of the inner surface of the window while substantially simultaneously preventing deposition of etch byproducts on the inner surface of the window.
The apparatus and methods of the present invention provide numerous advantages. Most notably, the apparatus and methods of the present invention uniformly prevent the deposition of electrically conductive reaction products, e.g., RuO2, on the inner surface of the upper wall (e.g., TCP window) of a chamber in an inductively coupled plasma etching system. This increases throughput in the plasma etching of recently developed device materials, e.g., Ru, because the plasma etching operation does not have to be stopped to clean the walls of the chamber after only a few wafers have been processed. In addition, the apparatus and methods of the present invention also uniformly prevent sputtering of the inner surface of the upper wall (e.g., TCP window) of a chamber in an inductively coupled plasma etching system. This increases the reproducibility of the process conditions by avoiding the generation of particles and the introduction of unwanted chemical species into the process environment.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.